Field of the Invention
The present invention relates to an image forming apparatus configured to form an image based on input image data.
Description of the Related Art
Hitherto, in regard to an electrophotographic image forming apparatus, control to cause a light-emitting element of a laser scanner to minutely emit light for a non-image area within a printable area to such an extent as not to cause adhesion of toner is proposed as a measure for solving various problems relating to the image forming apparatus. The non-image area represents an area within the printable area to which toner is not caused to adhere. The control to cause the light-emitting element of the laser scanner to minutely emit light to such an extent as not to cause adhesion of toner is referred to as “background exposure” or “non-image area minute light emission”. In contrast to the non-image area, an area within the printable area to which toner is caused to adhere is referred to as “visual image area”.
For example, in Japanese Patent Application Laid-Open No. 2003-312050, it is proposed to use the background exposure for the purpose of suppressing a white gap. For example, in an image of a cyan band and a black band that are made adjacent to each other, the cyan band and the black band are normally formed to be adjacent to each other without a gap. However, there is a phenomenon in which toner images in the respective colors are each formed to become thinner and a gap occurs between cyan and black in a final image formed on a recording material. This phenomenon is referred to as “white gap”. The thinning of the toner image within the visual image area, which may cause the white gap, is ascribable to an electric field is convoluted in an edge part of an electrostatic latent image formed on a photosensitive drum, and the background exposure is proposed as a method of preventing the thinning of the toner image. Further, in, for example, Japanese Patent Application Laid-Open No. 2013-117622, it is proposed to use the background exposure in order to eliminate nonuniformity in a potential of a photosensitive drum surface to which a charging voltage has been applied. In order to suppress an occurrence of a phenomenon called “sands” due to overcharging during the charging or a phenomenon called “ghost”, the background exposure is used to cause the non-image area to have a stable dark portion potential through the background exposure.
As a specific method for the background exposure, in Japanese Patent Application Laid-Open No. 2003-312050, it is proposed to superimpose minute light emission data, which is as small as not to form a toner image and has no correlation, on an input image, and to output the minute light emission data as a video. Further, in Japanese Patent Application Laid-Open No. 2013-117622, the background exposure is conducted by causing a bias current as small as to enable weak light emission to flow through a laser diode within the non-image area.
However, in Japanese Patent Application Laid-Open No. 2003-312050, image data has a pattern for a background exposure superimposed on the image, but the pattern for the background exposure is generated at random. Therefore, there may occur an error between an originally targeted surface potential of the photosensitive drum and an actual surface potential thereof, and the accuracy of a surface potential of the photosensitive drum may deteriorate. Further, in Japanese Patent Application Laid-Open No. 2013-117622, a laser is caused to emit light as small as not to form a toner image, and hence it is necessary to control the bias current with high accuracy. A bias current source of a laser driver configured to control a current flowing through the laser diode of the laser scanner or an APC circuit configured to conduct automatic light intensity control (hereinafter referred to as “APC”) requires highly accurate control, which may cause an increase in the size of the APC circuit or an increase in cost. In this manner, a circuit scale increases when the background exposure is conducted by the bias current, while the accuracy of potential control of the photosensitive drum deteriorates when the background exposure is conducted with the image data.